Question regarding Windsor Ontario built cars (70 Swinger)

hope these help... The black is probably part of the phosphate dip process.

http://www.mmcdetroit.com/ICCA/References/Chassis/

http://www.hamtramck-historical.com...DataBook/1967/67_Plymouth_Engineering0031.jpg

http://www.hamtramck-historical.com/images/dealerships/DealershipDataBook/1970/70_Dart0025.jpg